Okay, only works with old bulbs and its a trick-question not a puzzle


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I agree with you.
Ideally, if we are allowed to switch on 2 bulbs at a time then, turn any two switches on and check, then come down and turn one of the switch OFF, so 2 rounds
If only 1 switch can be turned ON at a time, even then 2 rounds, as we mark which bulb and switch was never turned ON!

If it’s puzzle, and you can’t physically access bulbs then answer is 2. else 1.


Well, the puzzle itself is very old.


Put irons in place of bulbs. Answer is 2.